Using Memcached to optimize vB hacks

As we all know, there are lots of great hacks here at vB.org, but some of them are certainly not written with large forums in mind. On my site, www.pentaxforums.com, which averages 1,200-2,000 simultaneous members, I would love to install every useful hack that I come across, but I can't really afford to have silly statistics and gimmicks add global queries to the database.

Many hacks have one or more of these issues:
-Add global database queries
-Use slow/redundant database queries
-Repetitively perform strenuous computations

I've therefore turned to Memcached to cache frequently-updated yet non-critical data in order to save queries and increase page generation time. I've applied this to the following hacks, just to name a few:
-Top poster on forum home (5 minute caching)
-Forumhome social group stats (5 minute caching)
-Moderated posts / subscribed threads in notifications (5 minute caching)
-Cyb advanced new posts (5 minute caching)

In addition, I use this for:
-Fully caching the current forum activity in index.php
-Fully caching the output of showgroups.php

All in all, I've saved a total of 5 queries on forumhome and 3 global queries by applying the cache, and also significantly reduced page generation time, which is the real biggie. For example, without caching, my forumhome would take about 0.30 seconds to generate. With caching, however, the generation time falls to about 0.07 seconds - that's over 4x faster!

I'd like to share with you the code I wrote to accomplish the caching. It assumes you have Memcached installed on your server. This particular code is for the forumhome top poster hack. As you can see, it's quite simple in structure, and can therefore easily be adapted to other hacks as well.

Here, $postcount['count'] and $threadcount['count'] is the data from the queries which ends up being cached. The nice thing is that even if the data is fetched from the cache and not the database, it can be accessed through the same variable. This is because you can store anything in memcache- even templates that have already been evaluated.

If you currently don't have memcached installed on your server, it's quite easy to install using PECL. To check if you have it installed, upload a script to your server that contains the following code:

it's good practice to add vbulletin options for the cache timeouts so you can keep things centralized, and $vbulletin->config for the memcached servers

you can substitute time() calls with the constant TIMENOW if you're inside vbulletin

only use my method for code with global queries or intensive computation! A trivial mysql query is usually faster than connecting to memcache and reading from it. Try running some basic benchmarks using microtime() to find out if caching is worth it.

Try to keep the individual data fragments you cache as small as possible. The smaller the data, the faster it can be fetched.

So, in conclusion, if used properly, this code can speed up your forum tremendously. If you have a big board, try giving it a spin! Also, if you're interested in reducing your server's memory load, look into installing APC for PHP. Note that on a production environment, it would be better to have a global memcache connection instead of initializing it every time you try fetching data.

I'm not going to post the whole thing as it's site specific and would likely break things on others' sites, but the general steps I followed are (note that there are other approaches as well, such as caching the entire query, but I figured it would be best performance-wise to just cache everything):

1. Strip out the navbar/header/footer from the SHOWGROUPS template
2. In showgroups.php, cache the evaled output of SHOWGROUPS in a variable called $HTML using the code model at the top of this thread
3. At the end of the file, print the output using GENERIC_SHELL. This will prevent caching of the navbar/header/footer, so that they are always current.

Note that if you use multiple styles that don't share the same graphics, you either have to set $cache['datafile'] = 'something' . $styleid, or use a global replace for image folder paths.

I've found that going through the datastore is much slower than this on-the-fly approach (which is still fine from a design standpoint as long as you use $vbulletin->config for the server info and an option setting for the caching time), since memcached isn't good at dealing with large amounts of data.